This invention relates to rail pads. Such pads are interposed between the lower surface of a railway rail and a foundation member on which the rail stands and to which it is usually secured. The rail foundation member may, for example, be a concrete or steel sleeper extending across the railway track, or a slab or plate, for example, running along the length of the rail.
The purpose of the rail pad is to protect the foundation member from impulsive and other loads from passing rail traffic; to compensate for any unevenness in the foundation member; and, where the rail is electrical, to provide electrical insulation between the rail and the foundation member.
Such rail pads were from their working disposition, subject to considerable potentially damaging forces as railway traffic passes along the rail supported by the pads, and the recurrent common problem with such pads was the damage so caused, and the inevitable need for frequent replacement at substantial cost.
To alleviate this problem it has been established that the provision of an elastomeric rail pad of generally rectangular plan configuration having an upper surface adapted to underlie the lower face of a rail, and a lower face adapted to overly a concrete rail foundation member in which the pad is studded on the upper side (underlying the rail) will substantially improve the attenuation of the rail foundation member from forces exerted by the rail due to traffic passing thereacross.
Whilst such an arrangement has been singularly effective in reducing damaging forces upon the pad and the foundation member therebelow, particularly when the foundation member or sleeper contains recesses or pockets to contain ant position the pads under the rail. In this purpose-built assembly, pads are able to withstand high vertical and side loading whilst providing shock attenuation and minimising track damage with no possibility of extrusion caused by side loading.
The improved behaviour resulting from the use of rail pads in flat sleeper assemblies can be outweighed by the tendency of pads to be extruded and xe2x80x9clostxe2x80x9d from under track by high side forces, this condition having particular effect when trains are negotiating bends in the track and when high axle loads are present.
It is especially to these conditions of track where sleepers do not have containment pockets from pads and also where high slide loads are present that the present invention is directed, and it is an object of the present invention to overcome or at least substantially reduce the problems identified above.
In accordance with the invention there is provided an elastomeric rail pad of generally rectangular plan configuration, the pad having an upper face adapted to underlie the lower face of a rail, and a lower face adapted to overly a concrete rail foundation member characterised in that the pad includes reinforcement means which is generally parallel to its mean plane, and extending at least between dispositions associated with generally opposing corners of the generally rectangular pad, said reinforcing means having a tensile strength such as to resist, in use of the pad, forces from traffic passing across the rail disposed thereabove otherwise tending to stretch the pad in the mean plane thereof.
The reinforcing means can be associated with the lower or upper faces of the pad, or elsewhere, but in one preferred embodiment may be associated with the lower face of the pad.
The reinforcing means may be of a sufficient tensile strength plastic, such as nylon, or a metal such as steel, and may be disposed within the pad by forming the pad about such reinforcement, or may comprise a member attached to, for example, the base of the pad.
The reinforcement means may comprise a member of any appropriate configuration to achieve the desired result hereinabove specified, and in one embodiment may be in the form of a cruciform extending between corners of the generally rectangular pad.
The pad can have smooth lower and/or upper surfaces, or the upper and optionally the lower surface can have an array of grooves, ridges, studs or other protrusions or recesses for the purpose of improving the cushioning properties of the pad.
The pad, in a preferred embodiment, may be of a single sided nature in that a plurality of protrusions to improve the attenuation of the rail foundation member may be disposed solely on the upper face of the pad. In this case, the reinforcement means typically is recessed into the lower face of the pad so as not to increase to overall height of the assembly. In other embodiments the reinforcing means may be disposed within the pad which then may be again of a single upper face protrusion laden pad, or may be both upper and lower protrusion laden.
The generally rectangular plan configuration of the rail pad may have rectangular recesses (in plan view) along two opposed sides midway along those sides, thereby defining on each end of such recesses what can be termed xe2x80x9cearxe2x80x9d portions of the pad which in use locate the pad with respect to the anchoring assembly thereof between the overlying rail and the underlying rail foundation member. In this case the reinforcing means may be configured such as to extend into the wings, thereby providing stiffness thereto, with significant affecting practice and preventive movement of the pad from its required disposition between the rail and rail support member.
In a further aspect, the invention provides a method of protecting a foundation member for a railway rail from impulsive and other loads from rail traffic passing over this rail, which method comprises positioning between the foundation member and the railway rail an elastomeric rail pad as hereinbefore defined.
In a still further aspect, the invention provides a method of preventing extrusion of a rail pad from between a foundation member and a railway rail, which method comprises providing the rail pad with reinforcing means as hereinbefore defined.